1. Field of the Invention
The present invention relates to a rubber composition and more particularly to a rubber composition in which a high hysteresis loss is achieved by the modification of an additive without impairment of other physical properties, such as fracture characteristics, a method of controlling the physical properties of the rubber, and a tire using the rubber composition.
2. Description of the Related Art
Proposed techniques for imparting a high hysteresis loss to a rubber composition or proposed techniques for preparing a rubber composition having a high hysteresis loss after vulcanization include (1) the addition of a large amount of carbon black, (2) use of a polymer having a high glass transition temperature (hereinafter referred to as “Tg”), and (3) the addition of a large amount of softener.
As a technique for improving the hysteresis loss of a rubber composition, for example, Japanese Unexamined Patent Application Publication No. 2000-109610 describes a rubber composition and a pneumatic tire in which the hysteresis loss of the rubber composition is increased by the addition of a predetermined amount of polymer prepared by cationic polymerization using a Lewis acid catalyst as an initiator to a rubber component without impairment of fracture characteristics. Japanese Unexamined Patent Application Publication No. 2003-213040 describes a technique for providing a rubber composition containing a rubber component and a predetermined softener composed of an asphalt and a process oil and thereby having a high hysteresis loss and high fracture resistance.
Furthermore, in a known technique, a carbon fiber grown from a vapor phase is added to a rubber composition to improve the physical properties of the rubber composition. For example, Japanese Unexamined Patent Application Publications Nos. 1-287151 and 1-289843 describe rubber compositions in which predetermined amounts of carbon fiber grown from a vapor phase and carbon black are added to a rubber component to improve their physical properties.
However, in the case of (1) the addition of a large amount of carbon black, while the hysteresis loss is increased after vulcanization, another important characteristic, elongation, becomes deteriorated. In the case of (2) use of a polymer having a high Tg, after vulcanization, the modulus of elasticity undesirably increases and the elongation at break decreases in an operating temperature range, that is, at low temperature. In the case of (3) the addition of a large amount of softener, after vulcanization, while the hysteresis loss and the elongation at break increase, the breaking strength and the anti-setting properties become much deteriorated.